1. Field
Embodiments of the inventive concept relate to a semiconductor device having a resistance changeable element and a bottom electrode.
2. Description of Related Art
Non-volatile memory devices are widely used in many consumer, commercial and other applications. While some non-volatile memory devices, such as flash memory, use accumulated charge to store data, some other memory devices, such as resistive random access memory (RRAM), phase change RAM (PRAM), and magnetic RAM (MRAM), use change in resistivity of a material therein to store data.
A resistive memory cell generally includes a bottom electrode, a top electrode, and a variable resistivity material connected therebetween. The resistive memory cell can be configured so that the resistivity of the material is controlled in response to a voltage that is applied between the first and second electrodes.
A PRAM device may include a phase changeable material layer which functions as a variable resistivity material. In response to sufficient heat, the phase changeable material layer may change phase so that its resistance changes and remains changed after its temperature returns to a pre-heating level. The phase changeable material layer may be formed from a chalcogenide material that includes germanium (Ge), antimony (Sb), and/or tellurium (Te). The phase of the material can be controlled in response to a level of current and/or duration of current that is applied to an electrode to heat the material a sufficient amount to change its phase. The resistance of the phase changeable material layer varies in response with its phase. For example, when the phase changeable material has a crystalline state, its resistance can be substantially less than when the phase changeable material layer has an amorphous state. Accordingly, the resistance of the phase changeable material in a PRAM device is controlled to store a logic value and is sensed to read the logic value.
To downscale non-volatile memory devices and improve their performance, research has been conducted on various methods for reducing the size of a bottom electrode. When forming a PRAM cell, it can be desirable to reduce the size of the bottom electrode and, thereby, a contact area between the bottom electrode and the phase-change material. However, reducing the size of the bottom electrode can degrade an electrical connection between the bottom electrode and associated diode. For example, reducing the contact area between the bottom electrode and the diode causes can degrade current drivability.
It is therefore desirable to develop a processes for fabricating a non-volatile memory device capable having improved current drivability of a bottom electrode, while minimizing a contact area between the bottom electrode and the phase-change material.